It was a just in case thing. I don’t think one has to be Mattir Neder here, especially because she points out that had it not been readily available then she never would have thought of keeping CY Lechumra. Thus, when she is somewhere where it is not readily available her “just in case” stringency probably wouldn’t apply.
Even if you would have to be Mattir Neder, you have to look at this two ways. Yes, it shows a submission to a physical desire. But we are human beings with physical desires and Muttar ways to fulfill those desires. If having this physical desire is actually harming your daily function and your Avodas Hashem, then it would be quite improper for you to avoid doing something Muttar.